The long-term goal of this study is to understand the role of oxidative stress in the aging process. Mitochondria have been widely hypothesized to play a key role in the causation of oxidative stress and aging in animals. This hypothesis has been based on the findings that mitochondria are the main intracellular producers of superoxide anion radical (O2-) and H2O2, which are the progenitors of a variety of other reactive oxygen species (ROS). Furthermore, the rates of mitochondrial O2- and H2O2 generation as well as amounts of mitochondrial oxidative damage increase with age, whereas oxidative phosphorylation capacity declines during aging. It has been shown that oxidative damage to mitochondria can cause both the age-related increase in O2- and H2O2 generation and the loss in respiratory capacity. The hypothesis that attenuation of mitochondrial oxidative damage will retard the progression of age-related deleterious alterations and extend the life span of the organism, will be tested in Drosophila melanogaster using transgenic approaches. Three different experimental strategies will be used to decrease the level of mitochondrial oxidative damage. The first will be to simultaneously overexpress Mn-SOD and ectopic catalase in the mitochondrial matrix; some lines of flies will additionally overexpress CuZn-SOD and catalase in the cytosol. Such overexpression of antioxidant enzymes should decrease the rates of mitochondrial O2- and H2O2 generation and lower the overall level of oxidative stress in cells. The second strategy will be to use regulatable gene promoters to overexpress SOD and catalase in order to control the timing and tissue-specificity of antioxidant gene overexpression. This approach may uncover beneficial effects of reduced oxidant production, which are masked by counterbalancing harmful effects of antioxidant elevation during sensitive stages of development. The third strategy will be to overexpress DNA glycosylase within the mitochondrial matrix to enhance DNA oxidative damage repair capacity. This latter approach is expected to result in an actual reversal of damage, whereas all previous strategies have concentrated on slowing the rate at which it accumulates. The effects of the different gene overexpression on age-related changes in mitochondria, and on the biochemical and physiological patterns of aging of the flies, including life spans, will be determined. The significance of this study is that it will provide a direct test of a basic tenet of the oxidative stress hypothesis of aging, namely that mitochondrial oxidative damage plays a key role in the aging process.